1. Field of the Invention
The present invention relates to a leadframe for use in a semiconductor device with built-in heat sink, and to a resin-sealed semiconductor device that uses the leadframe.
2. Related Art
In recent years, the miniaturization, high integration and high-density mounting of semiconductor components such as semiconductor devices has been sought in response to the miniaturization of electronic devices. This has resulted in the release of heat generated by semiconductor devices becoming a crucial issue.
Semiconductor devices with built-in heat sinks or exposed die pads have been proposed as a countermeasure to the problem of heat release in semiconductor devices. For example, Japanese Patent Application Publication No. 2001-15669 discloses a semiconductor device with built-in heat sink.
On the other hand, there is growing concern worldwide for the environment, which has lead to increasingly persistent calls for lead-free manufacturing also in relation to semiconductor devices.
However, with a conventional semiconductor device having a built-in heat sink (i.e. two-tiered frame), it is necessary to limit the amount of adhesive used when adhering a semiconductor element to the heat sink, possibly creating a gap between the heat sink and the semiconductor element. Even in the case of the semiconductor device being sealed using sealing resin, the resin does not run into the gap, leaving space for absorbed moisture to gather.
The mounting temperature when mounting a resin-sealed semiconductor device with built-in heat sink to a printed circuit board using lead-free solder is higher than for normal lead solder. This increases the temperature within the semiconductor device, which in turn raises the vapor pressure of absorbed moisture and promotes exfoliation of the semiconductor element from the heat sink, giving rise to the danger of internal bulging and cracking.